1. Field of the Invention
The present invention relates to a versatile production system and methods for operating the system. The system manufactures various kinds of products, including small quantities, on a single production line. The present system particularly relates to methods for operating the system by monitoring the running conditions of the production line and automatically generating work order sheets so as to increase productivity by minimizing tact time of the production line.
2. Description of the Invention
In general, in a production line for manufacturing products, necessary parts for assembling the products are supplied; the products are assembled, tested and inspected and the performance of the assembled products are approved based on the results of the test and are conveyed to a packing site. It is preferable for mass production to install a production line for each product. However, a large factory space and a large number of production facilities are required when many different products are being manufactured. Also products are manufactured in small quantities having a separate production line for each product, idle time increases, and sections of occupied factory space, production facilities, and operators become redundant.
In order to solve these problems, an applicant of the present invention developed inventions previously filed at the Japanese Patent Office, entitled "Versatile Production System" and referenced as Japanese patent application numbers 4-290314 and 4-291665, having U.S. application Ser. Nos. 08/024,210 and 08/022,026, respectively. According to this system, a production system is provided that manufactures various kinds of products, including small quantities. In the system, work order sheets required for each process and information pertaining to defective parts found in the preceding processes on the production line are automatically provided. In addition, the system automatically produces a test result report before conveying the products to a packing site.
In such a production system, there are three aspects that should be considered to improve productivity. The first aspect is "tact time". In the production line, tact time, is consumption time for executing each process, such as product assembling, testing and inspection. Tact time is different depending on the work efficiency or health conditions of each operator. The tact time changes depending on each operator's working time because the work efficiency changes depending on each operator's working time.
The second aspect is that continual production proceeds without knowing the manufacturing condition of defective products. A product is defective if it includes missing parts or defective units. Defects are found in the assembled and tested products.
When continual production proceeds without knowledge of the defects (that is, if abnormal conditions occur), productivity deteriorates significantly. If the continual production proceeds without knowing the percentage of defective products, a significant number of defective products will potentially be manufactured.
The third aspect is described below. In the production line, consumption time for executing each process (such as assembling, testing and inspecting) is different so that tact time, which is the maximum consumption time for executing each process, is preferably minimized, whereby each operator does not have excess time between each process. In order to minimize tact time, work order sheets are occasionally prepared for each operator at each working site. Work order sheets are prepared by trial and error based on manual calculations when work is assigned to operators at each work site. Production then proceeds in accordance with the work order sheets.
However, the work order sheets obtained above are usually inappropriate, thereby providing operators with idle time and reducing productivity. In addition, preparation of the work order sheets requires time and labor, thereby preventing the work order sheets from being prepared on time when work order changes are required from the production control system.